June 2, 2019 – Afternoon and evening mountain thunderstorms through Monday then decreased showers Tuesday. High snow levels. No shower activity across interior NorCal Wednesday through the end of the week. Warmer than normal temperatures through the first half of next week then closer to normal end of the week.
Discussion
Last of the shower activity over interior NorCal ended by midnight with skies mainly clear at this time. Upper low remains over southern California and is expected to remain in relatively the same position as it was on Saturday. With similar moisture and stability projections, expecting similar weather to Saturday. Therefore, thunderstorm development over the mountains a likelihood again starting mid to late afternoon. Northeast flow aloft may bring a risk of some Sierra shower activity down into the valley this evening as it has the last couple of evenings where trace amounts were reported on the valley floor. Much heavier showers will be possible at the higher elevations with PW values still forecast at well over an inch. More stable conditions will bring drop off in shower activity again this evening. Daytime highs today will be similar to Saturday depending on cloud cover.
The upper low shifts eastward slightly on Monday as weak high pressure pushes in over the state but stability and moisture values don’t change that much so not expecting a large overall change in the forecast. Therefore, another round of mountain showers on tap for Monday. Upper low center shifts over Arizona on Tuesday with weak high pressure taking over California. Models still prog high moisture and instability over the region so can not rule out afternoon showers over the northern Sierra closest to the departing low center. For the remainder of the CWA, warming airmass will nudge up high temperatures to about 10 degrees above normal. A trough pushes in to the Pacific Northwest by mid week bringing southwest flow aloft. This should bring drier more stable conditions for the start of a drier period going into the second half of the week.
Extended Discussion (Thursday through Sunday)
Upper level trough will be pushing into the PacNW to start the extended period. GEFS and Euro ensemble show the axis moving through later Thursday into Friday. Currently things look to remain dry with this but if we would see any activity it would likely be restricted to the northern higher elevations. Cooler temperatures set in Thursday and Friday and will be running a bit below average. Ridge builds in next weekend with a warming trend and valley highs returning to the 90s by Sunday.